Client Credentials Authentication with JWT in Rails APIs — A Practical Guide

Following up on our previous article - JWT Authentication in Rails APIs — Getting Started with System Integration - about basic JWT authentication for Rails APIs, it’s time to explore a more dynamic and secure approach using client credentials authentication — with and .

This model is widely used in API-to-API integrations and is a step forward from manually generated tokens.

In this guide, we’ll implement an endpoint () that issues JWT tokens based on valid client credentials, offering a scalable and professional authentication method for system integrations.

✨ Use Case Example

Your company provides an API for partners or internal systems. Instead of manually generating tokens, each partner has:

• A ` (public identifier)

• A ` (private key)

Partners authenticate using to get a JWT token, which grants access to protected endpoints.

🔧 Step 1 — Database Model: API Clients

Let's create a simple model to manage client credentials:

✅ Explanation:

• : Public identifier for the client (like a username).

• : Private credential (like a password).

• You can generate both using .

🔐 Step 2 — JWT Configuration

Set your secret key and algorithm for encoding tokens.

✅ Explanation:

• Centralizes JWT settings.

• Uses environment variables in production for security.

🚀 Step 3 — Token Issuer Service

Service to issue JWT tokens when credentials are valid.

✅ Explanation:

• Generates a token with and expiration time.

• The token can be verified without accessing the database every time.

🛡️ Step 4 — Token Verifier Service

Service to decode and validate the JWT token.

✅ Explanation:

• Verifies the token signature and expiration.

• Checks if the exists in the database.

🌐 Step 5 — API Routes

✅ Explanation:

• : Authentication endpoint to request a token.

• : Example of a protected endpoint.

🔑 Step 6 — Tokens Controller

Handles client credentials authentication and token generation.

✅ Explanation:

• Checks if the and are valid.

• Returns a JWT token if valid, or an error if not.

🔒 Step 7 — Base Controller with Authentication Filter

✅ Explanation:

• Validates the token before allowing access to any protected endpoint.

• The authenticated client is available as .

📦 Step 8 — Example Protected Endpoint

✅ Explanation:

• Example endpoint that requires a valid token to access product details.

🚀 How to Authenticate — Example Request

Request:

Response:

✅ Use this token in requests:

🔥 Key Benefits of This Approach

• More secure than hardcoded tokens.

• Easy to manage multiple clients (partners, internal systems, etc.).

• Supports token expiration and better security practices.

• Fully stateless — no session storage required.

✅ Conclusion

This pattern is widely adopted for system-to-system authentication in modern APIs.

With and , plus JWT, your API becomes more secure, scalable, and easy to integrate with external services.

💬 Would you like the next article on adding refresh tokens, token revocation, or best practices for API security? Let me know in the comments!